Coil testing apparatus



Feb. 12, 1935. B. J. HASKINS 1,990,487

COIL TESTING APPARATUS Filed Dec.- 9, 1933 Patented Feb 12, 1935 UNITEDSTATES PATENT orri' ca con. TESTING APPARATUS ofIllinois ApplicationDecember 9,

.1933, Serial No. 701,648

6 Claims. (Cl.175 18 3) An object of this invention is to provideapparatus for testing spark coils and the like where it is desirablethat not only will the time of flow of the charging current through thecoil be simulated for various equivalent engine speeds, but that thedifference in speed of opening thebreaker points shall be varied inaccordance with these same engine speeds in order that the conditionsshall approximate very closely those of actual operation of adistributor breaker on an automobile engine.

Another object is to provide means for com pensating for differences involtage of the battery on which the device is operated.

Another object is the simplification of coil testing apparatus.

These and other objects, as will hereinafter appear, are accomplished bythis invention which is fully described in the following specificationand shown in which Figure 1 is a schematic diagram of the apparatusshowing parts. of the motor and circuit breaker;

Fig. 2 is a greatly enlarged section through a part of the cam of thebreaker device; and

Fig. 3 is a graph showing the action of this device for automaticallycorrecting for battery voltage.

This is an improvement on the testing apparatus shown and described inmy application Serial No. 664,466, filed April 5, 1933.

The embodiment illustrated comprises a direct current motor which isshunt wound, as will later be described, so as to compensate for variousoperating voltages of a six volt storage battery 11 on which it isadaptedto operate. The motor has ashaft l2'upon which is keyed a cam 13which will later be described in detail as it contains the gist of thepresent invention.

A motor mechanism is associated with the cam 13 and has breaker points14 carried by the breaker arm 15 which is hingedly mounted at 16 and.carries a cam follower 17 which is constantly held against the face ofthe cam bymeans of a spring (not shown) A relatively stationary contactarm' 18 is also hingedly mounted at 16 and arries a nut 19 in which isthreaded a screw 20, t e screw carrying a pointer 21 operable over adial 22 so as to indicate the position of the'contact arm '18. The cam13 is preferably cylindrical except for alow v-shaped notch 13' which isformed therein, as shown in greatly enlarged detail in 2. The camrotates in a clockwise direction and the cam follower, shown in dottedlines in Fig.2, enters the notch at the right side to a depth permittedby the adjustment of the screw at which the points 14 will be incontact. As the cam continues to rotate the follower will:

the accompanying drawing, in

strike the left hand portion of the cam notch,

thereby separating the breaker points.

It is desirable in making a test of a spark coil, such as will later bedescribed, that the testing apparatus shouldbe capable of adjustment soas to vary the simulated engine speed from avery high speed to a pointapproximately one-half that speed. To do this I arbitrarily take twopoints A, A to represent the opening and closing points, respectively,of the cam and separate these by an angle of 20 on the cam, these pointscorresponding to the opening and closing points of the cam for thehighest equivalent engine speed desired.

The angle 0 may be taken as the lowest angle to be used on this cam andthis angle may be calculated on thebasis of a lift of .002" at thebreaker points for each 1 of are at the cam. If I take the follower aslocated half way .between the breaker points and the fulcrum, the riseat.

the follower, that is, on the cam, will be one-half that; at the points,or .001" per 1 of arc of the cam. The average diameter of the cam at thepoints of opening may be taken as By calculating the angle of the cainface at C, I find that the tangent of the angle 0 is approximately .001"divided by .0066, or .15. The angle 0 is accordingly about 8, 30'. Bydoubling this angle for point A, the angle a is 17, and by taking anaverage of these two angles ,for the point B, I obtain the angle b as12, 45'.

By properly choosing the points A, B and C and drawing tangentscorresponding to these angles through them and connecting up thesetangents to make a smooth curve, I have constructed the opening face ofthe cam. The angles on the cam face (Fig. 2) are exaggerated for thesake of greater clearness.

Knowing the cam angle of A to be 20, that of B 30, and that of C 40, thecorresponding points of closing A, B and C are found by plotting theseangles alongthe concentric circles through the points A, B and C. Asmooth curve A, B, C is then drawn and is extended to the point D whereit joins up with the extended endofthe curve through A, B, C. I

, Thus it will be seen that by operating with the follower 17 on theradius through. the points C, C, the breaker points will remain closedfor 40 of cam arc corresponding to a slow engine speed, and the tangentof the angle 0 being small gives a relatively slow opening in the-pointsalso corresponding -to a .slow engine speed.- however, the follower isreadjusted so as to cause it to operate on the line through the pointsA, A,

Likewise as the follower strikesat a much more rapid rate owing to thefact that the tangent of the angle a is substantially double the tangentof the angle 0. Thus as the angle of cam through which the points remainclosed is halved, that is cut from 40 to 20, the rate of opening thebreaker points is doubled. While the rotative speed of the cam remainsconstant this corresponds to the action which takes place in the usualdistributor breaker when the speed of the breaker cam is doubled. Inthat case, the time during which current flows through the primary ofthe coil under test is dependent on the speed of the distributor cam,and the speed with which the breaker points open is likewise dependenton the speed of that cam. That is, in the usual distributor breaker asthe cam speed is doubled the time during which current flows through theprimary of the coil is reduced by half, and the speed of opening thecircuit is doubled. Both those conditions are now accurately simulatedby this cam notch.

As a means for accurately and conveniently setting the breaker pointsfor any predetermined.

cam angle as 20, I have provided a collar 23 which may be adjustablysecured on the outer end of the shaft 12 by means of a nut 24. The

collar carries two markings at 0 and 20 on its outer face correspondingaccurately to this angle on the collar. To adjust the breaker to thesemarkings the shaft 12 is turned until the points are just closing, whichcorresponds to the position A of Fig. 2. The nut 24 is then loosened andthe collar turned on the shaft until the 20 marking on the periphery ofthe collar lies in front of a mark (not shown) on the end of the motorhousing, or the like. The nut 24 is then tightened. The zero marking isthen set to correspond to the position of opening of the breaker points.It may be necessary to adjust the screw 20 to make the points of openingcoincide with the marking 0 and 20 on the-collar.

During this time the pointer 21, if the screw 20 and parts associatedtherewith are properly adjusted, will be likewise pointing at the 20marking on the scale 22. The shaft 12 is then rotated until the 20marking on the collar 23 comes into alignment with the marking on themotor housing. When this occurs the points 14 should just start to open.If not, the screw 20 will have to, be readjusted so as to make thebreaker points open and close in accordance with the marks 0 and 20 onthe collar 23.

Having adjusted the parts so that the pointer 21 stands at 20 on thedial 22 when the breaker points are closing and opening at 0 and 20 onthe collar 23, the pitch of the screw 20 is such that the position ofthe pointer 21 will accurately indicate on the dial other settings offrom 20 to 40 of the cam during which the breaker points are closed.

In order to compensate for various voltages of the storage battery I usea motor 10 which is shunt wound and which preferably has in seriestherewith a resistor R whose resistance is about twenty percent that ofthe resistance of the motor .at normal operative speeds. This motor isso wound that with a battery voltage of 6 volts it has a speed of 1200R. P. M. and at 7 volts a speed of 1450 R. P. M.

Thus the higher voltage gives a higher amperage through the primarywinding of the spark coil which means a higher rate of energization ofthe coil. The higher voltage, however, means a higher speed for theshaft 12 and cam '13, and hence a shorter time during which the highercurrent flows through the spark coil. The two variables thus offset eachother and substantially equal energizations of the coil are obtainedwith different battery voltages.

In order to test a spark coil E having the usual primary and secondarywindings, the storage battery 11 is connected through leads 25, 26 withthe primary winding of the spark coil, and thence back through leads 27,28 to the breaker arm 15 where the circuit ,is grounded while the pointsare in contact, and then back from the ground 29 through the lead 30 tothe storage battery.

The secondary winding of the spark coil connects through a lead 32 withan electrode 33 of a spark gap 34, the opposite electrode 35 connectingthrough leads 36, 3'7 with the ground 29.

the time of closing the spark breaker points, but

also the faster opening thereof at higher engine speeds.

The reason for changing the speed of opening the breaker points varieswith engine speed is that at low speeds the points open slowly and anarc forming can follow the points. To overcome this a condenser isplaced across the points. If the points open quickly enough, no arc canfollow, and hence no condenser would be needed. In actual practice,however, this is not practicable, and a condenser is used to absorb thespark. The present invention simulates these actual operating conditionswhich obtain in the distributor of an automobile wherein the higher thespeed of the distributor shaft the faster the breaker points open. Thisis accomplished by the V-shaped cam notch having an arcuate openingface, as previously described.

In Fig. 3 is illustrated diagrammatically the action of the, motor inautomatically correcting for battery voltage. Thus a storage batteryhaving a potential of six volts will drive the motor at a speed of 1200R. P. M. If now we assume the angle of contact of the cam 13 duringwhich the breaker points are in contact is 40, the actual time that theyare in contact is about .005 seconds. It is found that current from thestorage battery at six volts flowing for .005 seconds will so energize aparticular spark coil that discharge of the secondary will show amomentary current of two amperes, which gives very satisfactoryoperation for this coil in an-automobile ignition system.

I, therefore, plot the point F corresponding to .005 seconds in time and2.0 amperes, and draw a horizontal line G through the point F. Thisline-(shown dotted) is a line of desired saturation for this spark coil.The line H, F represents roughly the saturation of the .0011 atdifferent time intervals during which current flows under a potential ofsix volts from .000 seconds to .005 seconds of breaker point closure.

It now the battery potential is raised to seven volts and the time ofclosure of the breaker points remained the same, the saturation wouldincrease so that the discharge of the coil would about .004 seconds. Ifnow we draw a straight line between H and J we see that-it crosses theordinate .004 at the, point K which is substantially on the horizontalline G of ,desired saturation. Thus the energization of the coil remainsnearly the same for different battery volt-' ages within the normaloperating range of six volts to seven volts. The above figures are forillustrative purposes only and are approximately correct for one type ofspark coil. Tests of various spark coils show that the principle hereinstated is substantially correct.

The combination of the shunt wound motor which compensates for batteryvoltage with the V-shaped cam notch of Fig. 2 provides a coil testerwhich is not only very efficient and accurate, but very simple andinexpensive to build and to operate. By this simple combination I amable to dispense with a battery voltmeter, a speed indicator for themotor, a motor speed regulatorfand a compensator for adjustingthe pointsof the spark gap to compensate for differences in battery voltages.

I claim:

1. In testing apparatus of the class described, a motor having a shaft,a make and break device having a cam on said shaft, said make and breakdevice having points adapted to be connected in series circuit with asource of direct current and with the primary winding of a spark coil tobe tested, a spark gap adapted to be connected in series circuit withthe secondary winding of the .spark coil, the cam having a low V- shapednotch in its face, a cam follower bearing on the face of the cam andoperable to close and open the make and break device as it passesthrough said notch, and means for varying the depth to which saidfollower entersthe notch to simulate various equivalent engine speedsfor the breaker device, the opening side of the cam notch being arcuateto increase the'rate of lift,

of the follower as the follower is lowered into the notch for thepurpose specified.

2. In testing apparatus of the class'described, a motor having a shaft,a make and break device having a cam on said shaft, said make and breakdevice having points adapted to be con-- nected in series circuit withthe source of direct current and with the primary winding of a sparkcoil to be tested, a spark gap adapted to be connected in series circuitwith the secondary winding of the spark coil, the cam having a low V-shaped notch in its face, a cam follower bearing on the face of the camand operable to close and open the make and break device as it passesthrough said notch, and means for varying the depth to which saidfollower enters the notch to simulate various equivalent engine speedsfor the breaker device, the opening side of the cam notchbeing arcuateto increase the rate of lift of the follower in substantially inverseratio to the cam angle during which the breaker points are closed.

3. In testing apparatus of the class described, a shunt wound mot-oradapted to be driven by a storage battery, said motor having a shaft, amake and break device having a cam on said shaft, said make and breakdevice having breaker points adapted to be placed in series circuit withsaid storage battery and with the primary winding of a spark coil to betested, a spark gap adapted to be connected in series circuit with thesecondary winding of the spark coil, the cam having a low V-shaped notchin its face, a cam follower bearing on the face of the cam and operableto close and open the make and break device as it passes through saidnotch, the angle of the cam on the closing side being lower than theangle of the cam on the opening side so as to give a quick opening ofthe breaker points.

'4. In testing apparatus of the class described, a shunt wound motoradapted to be driven by a storage battery, said motor having a shaft, amake and break device having a cam on said shaft, said make and breakdevice having breaker points adapted to be placed in series circuit withsaid storage battery and with the primary winding of a spark coil to betested, a spark gap adapted to be connected in series circuit with thesecnotch to simulate various equivalent engine speeds for the breakerdevice, the angle of the cam on the closing side being lower than theangle of the cam on the opening side so as to give a quick opening ofthe breaker points.

5. In testing apparatus of the class described,

a shunt wound motor adapted to be driven by a storage battery, saidmotor having a shaft, 9. make and break device having a cam on saidshaft, said make and break device having breaker points adapted to beplaced in series circuit with said storage battery and with the primarywind- .ing of a spark-coil to be tested, a spark gap adapted to beconnected in series circuit with the secondary. winding of the sparkcoil, the cam having a low V-shaped notch in its face, a cam followerbearing on the face of the cam and operable to close and open the makeand break device as it passes through said notch, the opening side ofthe cam notch being arcuate to increase the rate of lift of the followerinsubstantially inverse ratio to the cam angle during which the breakerpoints are closed. I

6. In testing apparatus of the class. described, a shunt wound motorhaving a shaft, a make and break device having a cam on said shaft,said: make and break device having points adapted to be connected inseries circuit with a .source of direct current and with the primarywinding of a spark coil to be tested, a spark gap adapted to beconnected in series circuit with the secondary winding of the sparkcoil, the cam having a low V-shaped notch in its face, a cam followerbearing on the face of the cam and oper-' BUTLER J. HASKINS.

